[PATCH] docs: kernel-hacking: discourage from calling disable_irq() in atomic

[PATCH] docs: kernel-hacking: discourage from calling disable_irq() in atomic

[A. Sverdlin]

From: Alexander Sverdlin <alexander.sverdlin@siemens.com>

Correct the example in documentation so that disable_irq() is not being
called in atomic context and remove the comment allowing to do so "with
care" from the function header itself.

disable_irq() calls sleeping synchronize_irq(), it's not allowed to call
them in atomic context.

Link: https://lore.kernel.org/lkml/87k02wbs2n.ffs@tglx/
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
---
 Documentation/kernel-hacking/locking.rst                    | 4 ++--
 Documentation/translations/it_IT/kernel-hacking/locking.rst | 4 ++--
 kernel/irq/manage.c                                         | 2 --
 3 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/Documentation/kernel-hacking/locking.rst b/Documentation/kernel-hacking/locking.rst
index 6805ae6e86e65..95fd6e0900d92 100644
--- a/Documentation/kernel-hacking/locking.rst
+++ b/Documentation/kernel-hacking/locking.rst
@@ -1274,11 +1274,11 @@ Manfred Spraul points out that you can still do this, even if the data
 is very occasionally accessed in user context or softirqs/tasklets. The
 irq handler doesn't use a lock, and all other accesses are done as so::
 
-        spin_lock(&lock);
+        mutex_lock(&lock);
         disable_irq(irq);
         ...
         enable_irq(irq);
-        spin_unlock(&lock);
+        mutex_unlock(&lock);
 
 The disable_irq() prevents the irq handler from running
 (and waits for it to finish if it's currently running on other CPUs).
diff --git a/Documentation/translations/it_IT/kernel-hacking/locking.rst b/Documentation/translations/it_IT/kernel-hacking/locking.rst
index 51af37f2d6210..bfbada56cf351 100644
--- a/Documentation/translations/it_IT/kernel-hacking/locking.rst
+++ b/Documentation/translations/it_IT/kernel-hacking/locking.rst
@@ -1309,11 +1309,11 @@ se i dati vengono occasionalmente utilizzati da un contesto utente o
 da un'interruzione software. Il gestore d'interruzione non utilizza alcun
 *lock*, e tutti gli altri accessi verranno fatti così::
 
-        spin_lock(&lock);
+        mutex_lock(&lock);
         disable_irq(irq);
         ...
         enable_irq(irq);
-        spin_unlock(&lock);
+        mutex_unlock(&lock);
 
 La funzione disable_irq() impedisce al gestore d'interruzioni
 d'essere eseguito (e aspetta che finisca nel caso fosse in esecuzione su
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 40fe7806cc8c9..2054de5bf3c53 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -722,8 +722,6 @@ EXPORT_SYMBOL(disable_irq_nosync);
  *	This function waits for any pending IRQ handlers for this interrupt
  *	to complete before returning. If you use this function while
  *	holding a resource the IRQ handler may need you will deadlock.
- *
- *	This function may be called - with care - from IRQ context.
  */
 void disable_irq(unsigned int irq)
 {
-- 
2.34.1

Re: [PATCH] docs: kernel-hacking: discourage from calling disable_irq() in atomic

[Manfred Spraul]

Hi Alexander,

On 12/12/22 17:37, A. Sverdlin wrote:
> From: Alexander Sverdlin <alexander.sverdlin@siemens.com>
>
> Correct the example in documentation so that disable_irq() is not being
> called in atomic context and remove the comment allowing to do so "with
> care" from the function header itself.
>
> disable_irq() calls sleeping synchronize_irq(), it's not allowed to call
> them in atomic context.
>
> Link: https://lore.kernel.org/lkml/87k02wbs2n.ffs@tglx/
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>

Reviewed-by: Manfred Spraul <manfred@colorfullife.com>

(but check below, I would prefer if the change to kernel/irq/manage.c is 
dropped.

> ---
>   Documentation/kernel-hacking/locking.rst                    | 4 ++--
>   Documentation/translations/it_IT/kernel-hacking/locking.rst | 4 ++--
>   kernel/irq/manage.c                                         | 2 --
>   3 files changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/kernel-hacking/locking.rst b/Documentation/kernel-hacking/locking.rst
> index 6805ae6e86e65..95fd6e0900d92 100644
> --- a/Documentation/kernel-hacking/locking.rst
> +++ b/Documentation/kernel-hacking/locking.rst
> @@ -1274,11 +1274,11 @@ Manfred Spraul points out that you can still do this, even if the data
>   is very occasionally accessed in user context or softirqs/tasklets. The
>   irq handler doesn't use a lock, and all other accesses are done as so::
>   
> -        spin_lock(&lock);
> +        mutex_lock(&lock);
>           disable_irq(irq);
>           ...
>           enable_irq(irq);
> -        spin_unlock(&lock);
> +        mutex_unlock(&lock);
>   
>   The disable_irq() prevents the irq handler from running
>   (and waits for it to finish if it's currently running on other CPUs).
> diff --git a/Documentation/translations/it_IT/kernel-hacking/locking.rst b/Documentation/translations/it_IT/kernel-hacking/locking.rst
> index 51af37f2d6210..bfbada56cf351 100644
> --- a/Documentation/translations/it_IT/kernel-hacking/locking.rst
> +++ b/Documentation/translations/it_IT/kernel-hacking/locking.rst
> @@ -1309,11 +1309,11 @@ se i dati vengono occasionalmente utilizzati da un contesto utente o
>   da un'interruzione software. Il gestore d'interruzione non utilizza alcun
>   *lock*, e tutti gli altri accessi verranno fatti così::
>   
> -        spin_lock(&lock);
> +        mutex_lock(&lock);
>           disable_irq(irq);
>           ...
>           enable_irq(irq);
> -        spin_unlock(&lock);
> +        mutex_unlock(&lock);
>   
>   La funzione disable_irq() impedisce al gestore d'interruzioni
>   d'essere eseguito (e aspetta che finisca nel caso fosse in esecuzione su

> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index 40fe7806cc8c9..2054de5bf3c53 100644
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -722,8 +722,6 @@ EXPORT_SYMBOL(disable_irq_nosync);
>    *	This function waits for any pending IRQ handlers for this interrupt
>    *	to complete before returning. If you use this function while
>    *	holding a resource the IRQ handler may need you will deadlock.
> - *
> - *	This function may be called - with care - from IRQ context.
>    */
>   void disable_irq(unsigned int irq)
>   {

Can you drop this part?

I haven't noticed that you added this change into the patch, and thus I 
created a seperate patch.

https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kernel-irq-managec-disable_irq-might-sleep.patch

As core difference: I've added a might_sleep() into disable_irq().


--

     Manfred

[tip: irq/core] docs: locking: Discourage from calling disable_irq() in atomic

[tip-bot2 for Alexander Sverdlin]

The following commit has been merged into the irq/core branch of tip:

Commit-ID:     379af13b31fa8a36ad4abd59a5c511f25c5d4d42
Gitweb:        https://git.kernel.org/tip/379af13b31fa8a36ad4abd59a5c511f25c5d4d42
Author:        Alexander Sverdlin <alexander.sverdlin@siemens.com>
AuthorDate:    Mon, 12 Dec 2022 17:37:15 +01:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Wed, 11 Jan 2023 19:45:26 +01:00

docs: locking: Discourage from calling disable_irq() in atomic

Correct the example in the documentation so that disable_irq() is not being
called in atomic context.

disable_irq() calls sleeping synchronize_irq(), it's not allowed to call
them in atomic context.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Manfred Spraul <manfred@colorfullife.com>
Cc: linux-doc@vger.kernel.org
Link: https://lore.kernel.org/lkml/87k02wbs2n.ffs@tglx/
Link: https://lore.kernel.org/r/20221212163715.830315-1-alexander.sverdlin@siemens.com

---
 Documentation/kernel-hacking/locking.rst                    | 4 ++--
 Documentation/translations/it_IT/kernel-hacking/locking.rst | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/Documentation/kernel-hacking/locking.rst b/Documentation/kernel-hacking/locking.rst
index c756786..dff0646 100644
--- a/Documentation/kernel-hacking/locking.rst
+++ b/Documentation/kernel-hacking/locking.rst
@@ -1277,11 +1277,11 @@ Manfred Spraul points out that you can still do this, even if the data
 is very occasionally accessed in user context or softirqs/tasklets. The
 irq handler doesn't use a lock, and all other accesses are done as so::
 
-        spin_lock(&lock);
+        mutex_lock(&lock);
         disable_irq(irq);
         ...
         enable_irq(irq);
-        spin_unlock(&lock);
+        mutex_unlock(&lock);
 
 The disable_irq() prevents the irq handler from running
 (and waits for it to finish if it's currently running on other CPUs).
diff --git a/Documentation/translations/it_IT/kernel-hacking/locking.rst b/Documentation/translations/it_IT/kernel-hacking/locking.rst
index b8ecf41..05d362b 100644
--- a/Documentation/translations/it_IT/kernel-hacking/locking.rst
+++ b/Documentation/translations/it_IT/kernel-hacking/locking.rst
@@ -1307,11 +1307,11 @@ se i dati vengono occasionalmente utilizzati da un contesto utente o
 da un'interruzione software. Il gestore d'interruzione non utilizza alcun
 *lock*, e tutti gli altri accessi verranno fatti così::
 
-        spin_lock(&lock);
+        mutex_lock(&lock);
         disable_irq(irq);
         ...
         enable_irq(irq);
-        spin_unlock(&lock);
+        mutex_unlock(&lock);
 
 La funzione disable_irq() impedisce al gestore d'interruzioni
 d'essere eseguito (e aspetta che finisca nel caso fosse in esecuzione su